The present invention relates to a temperature control system for controlling the temperature of a heat roller provided in a printer employing an electrophotographic image transfer system.
The printer employing an electrophotographic image transfer system includes an exposure step for forming an electrostatic latent image on the circumferential surface of a photoreceptor drum, a developing step for adhering toner to the electrostatic latent image, a transfer step for transferring the toner image to a recording sheet, and a fixing step for fixing the toner image thus transferred to the recording sheet.
As the fixing means, a mechanism is generally employed for feeding the recording sheet between a heat roller heated to a high temperature and an oppositely arranged press roller, so as to fix the toner image to the recording sheet by thermocompression adhesion.
The heat roller is heated by a heat source such as a halogen lamp provided therein. In the case of a printer, for instance, the lamp is controlled so that a high fixing temperature is used only during the time when data is transmitted from a host computer, whereas a low standby temperature is used when no data exists after printing is terminated, in order to save electric power or suppress a temperature rise in the printer.
Since the aforementioned temperature control is performed within a range of 10 degrees, however, the actual heat roller temperature varies within the range.
When a certain period of time has elapsed after printing is terminated and the fixing temperature is lowered to the standby temperature, there occurs a difference between the temperature in cases where the upper limit of the fixing temperature is employed as a start point and where the lower limit thereof is used as a start point.
If, however, the temperature is lowered to the standby temperature a long time after it is switched to the standby temperature, warm-up time is unaffected in either case (i.e. upper or lower limit as start point) when the temperature is lowered.
When the switching of the fixing condition of the heat roller to the standby condition thereof is frequently made as in a case where data is transmitted to the printer intermittently, that is, when the temperature is raised again before it reaches the standby temperature, a problems arises in that long warm-up time is needed, when the lower limit of the fixing temperature is set as the start point at the time the temperature is lowered.